Merge pull request #587 from ucb-bar/ahb-fix

ahb: rewrote TLToAHB to avoid retracting requests on stall

src/main/scala/diplomacy/Parameters.scala

@@ -219,3 +219,20 @@ object AddressSet
     if (out.size != n) unify(out) else out.toList
   }
 }
+
+case class BufferParams(depth: Int, flow: Boolean, pipe: Boolean)
+{
+  require (depth >= 0)
+  def isDefined = depth > 0
+  def latency = if (isDefined && !flow) 1 else 0
+}
+
+object BufferParams
+{
+  implicit def apply(depth: Int): BufferParams = BufferParams(depth, false, false)
+
+  val default = BufferParams(2)
+  val none    = BufferParams(0)
+  val flow    = BufferParams(1, true, false)
+  val pipe    = BufferParams(1, false, true)
+}

src/main/scala/uncore/ahb/Test.scala

@@ -16,7 +16,7 @@ class RRTest1(address: BigInt)(implicit p: Parameters) extends AHBRegisterRouter
   new AHBRegBundle((), _)    with RRTest1Bundle)(
   new AHBRegModule((), _, _) with RRTest1Module)
 
-class AHBFuzzNative()(implicit p: Parameters) extends LazyModule
+class AHBFuzzNative(aFlow: Boolean)(implicit p: Parameters) extends LazyModule
 {
   val fuzz  = LazyModule(new TLFuzzer(5000))
   val model = LazyModule(new TLRAMModel("AHBFuzzNative"))
@@ -25,7 +25,7 @@ class AHBFuzzNative()(implicit p: Parameters) extends LazyModule
   val gpio  = LazyModule(new RRTest0(0x100))
 
   model.node := fuzz.node
-  xbar.node := TLToAHB()(TLDelayer(0.1)(model.node))
+  xbar.node := TLToAHB(aFlow)(TLDelayer(0.1)(model.node))
   ram.node  := xbar.node
   gpio.node := xbar.node
 
@@ -34,12 +34,12 @@ class AHBFuzzNative()(implicit p: Parameters) extends LazyModule
   }
 }
 
-class AHBNativeTest()(implicit p: Parameters) extends UnitTest(500000) {
+class AHBNativeTest(aFlow: Boolean)(implicit p: Parameters) extends UnitTest(500000) {
-  val dut = Module(LazyModule(new AHBFuzzNative).module)
+  val dut = Module(LazyModule(new AHBFuzzNative(aFlow)).module)
   io.finished := dut.io.finished
 }
 
-class AHBFuzzMaster()(implicit p: Parameters) extends LazyModule
+class AHBFuzzMaster(aFlow: Boolean)(implicit p: Parameters) extends LazyModule
 {
   val node  = AHBOutputNode()
   val fuzz  = LazyModule(new TLFuzzer(5000))
@@ -47,9 +47,9 @@ class AHBFuzzMaster()(implicit p: Parameters) extends LazyModule
 
   model.node := fuzz.node
   node :=
-    TLToAHB()(
+    TLToAHB(aFlow)(
     TLDelayer(0.2)(
-    TLBuffer(TLBufferParams.flow)(
+    TLBuffer(BufferParams.flow)(
     TLDelayer(0.2)(
     model.node))))
 
@@ -71,7 +71,7 @@ class AHBFuzzSlave()(implicit p: Parameters) extends LazyModule
   ram.node :=
     TLFragmenter(4, 16)(
     TLDelayer(0.2)(
-    TLBuffer(TLBufferParams.flow)(
+    TLBuffer(BufferParams.flow)(
     TLDelayer(0.2)(
     AHBToTL()(
     node)))))
@@ -83,9 +83,9 @@ class AHBFuzzSlave()(implicit p: Parameters) extends LazyModule
   }
 }
 
-class AHBFuzzBridge()(implicit p: Parameters) extends LazyModule
+class AHBFuzzBridge(aFlow: Boolean)(implicit p: Parameters) extends LazyModule
 {
-  val master = LazyModule(new AHBFuzzMaster)
+  val master = LazyModule(new AHBFuzzMaster(aFlow))
   val slave  = LazyModule(new AHBFuzzSlave)
 
   slave.node := master.node
@@ -95,7 +95,7 @@ class AHBFuzzBridge()(implicit p: Parameters) extends LazyModule
   }
 }
 
-class AHBBridgeTest()(implicit p: Parameters) extends UnitTest(500000) {
+class AHBBridgeTest(aFlow: Boolean)(implicit p: Parameters) extends UnitTest(500000) {
-  val dut = Module(LazyModule(new AHBFuzzBridge).module)
+  val dut = Module(LazyModule(new AHBFuzzBridge(aFlow)).module)
   io.finished := dut.io.finished
 }

src/main/scala/uncore/ahb/ToTL.scala

@@ -56,7 +56,7 @@ class AHBToTL()(implicit p: Parameters) extends LazyModule
       val d_addr  = Reg(in.haddr)
       val d_size  = Reg(in.hsize)
 
-      when (out.d.valid) { d_recv := Bool(false); d_error := d_error || out.d.bits.error }
+      when (out.d.valid) { d_recv := Bool(false) }
       when (out.a.ready) { d_send := Bool(false) }
 
       val a_count  = RegInit(UInt(0, width = 4))
@@ -87,14 +87,12 @@ class AHBToTL()(implicit p: Parameters) extends LazyModule
 
       when (a_accept) {
         a_count := a_count - UInt(1)
-        d_error := d_error || !a_legal
         when ( in.hwrite) { d_send := Bool(true) }
         when (!in.hwrite) { d_recv := Bool(true) }
         when (a_first) {
           a_count := Mux(a_burst_ok, a_burst_mask >> log2Ceil(beatBytes), UInt(0))
           d_send  := a_legal
           d_recv  := a_legal
-          d_error := !a_legal
           d_pause := Bool(false)
           d_write := in.hwrite
           d_addr  := in.haddr
@@ -111,7 +109,11 @@ class AHBToTL()(implicit p: Parameters) extends LazyModule
       out.a.bits.data    := in.hwdata
       out.a.bits.mask    := maskGen(d_addr, d_size, beatBytes)
 
-      // Save the error for the last beat (so the master can't cancel the burst)
+      d_error :=
+        (d_error  && !(a_first && in.hready)) || // clear error when a new beat starts
+        (a_accept && !a_legal)                || // error if the address requested is illegal
+        (out.d.valid && out.d.bits.error)        // error if TL reports an error
+
       // When we report an error, we need to be hreadyout LOW for one cycle
       val inject_error = d_last && (d_error || (out.d.valid && out.d.bits.error))
       when (inject_error) { d_pause := Bool(true) }

src/main/scala/uncore/apb/Test.scala

@@ -16,7 +16,7 @@ class RRTest1(address: BigInt)(implicit p: Parameters) extends APBRegisterRouter
   new APBRegBundle((), _)    with RRTest1Bundle)(
   new APBRegModule((), _, _) with RRTest1Module)
 
-class APBFuzzBridge()(implicit p: Parameters) extends LazyModule
+class APBFuzzBridge(aFlow: Boolean)(implicit p: Parameters) extends LazyModule
 {
   val fuzz  = LazyModule(new TLFuzzer(5000))
   val model = LazyModule(new TLRAMModel("APBFuzzMaster"))
@@ -28,9 +28,9 @@ class APBFuzzBridge()(implicit p: Parameters) extends LazyModule
   ram.node  := xbar.node
   gpio.node := xbar.node
   xbar.node :=
-    TLToAPB()(
+    TLToAPB(aFlow)(
     TLDelayer(0.2)(
-    TLBuffer(TLBufferParams.flow)(
+    TLBuffer(BufferParams.flow)(
     TLDelayer(0.2)(
     model.node))))
 
@@ -39,7 +39,7 @@ class APBFuzzBridge()(implicit p: Parameters) extends LazyModule
   }
 }
 
-class APBBridgeTest()(implicit p: Parameters) extends UnitTest(500000) {
+class APBBridgeTest(aFlow: Boolean)(implicit p: Parameters) extends UnitTest(500000) {
-  val dut = Module(LazyModule(new APBFuzzBridge).module)
+  val dut = Module(LazyModule(new APBFuzzBridge(aFlow)).module)
   io.finished := dut.io.finished
 }

src/main/scala/uncore/axi4/Buffer.scala

@@ -4,22 +4,26 @@ package uncore.axi4
 
 import Chisel._
 import chisel3.internal.sourceinfo.SourceInfo
+import chisel3.util.IrrevocableIO
 import config._
 import diplomacy._
 import scala.math.{min,max}
 
 // pipe is only used if a queue has depth = 1
-class AXI4Buffer(aw: Int = 2, w: Int = 2, b: Int = 2, ar: Int = 2, r: Int = 2, pipe: Boolean = true)(implicit p: Parameters) extends LazyModule
+class AXI4Buffer(
+  aw: BufferParams,
+  w:  BufferParams,
+  b:  BufferParams,
+  ar: BufferParams,
+  r:  BufferParams)(implicit p: Parameters) extends LazyModule
 {
-  require (aw >= 0)
+  def this(aw: BufferParams, br: BufferParams)(implicit p: Parameters) = this(aw, aw, br, aw, br)
-  require (w  >= 0)
+  def this(x: BufferParams)(implicit p: Parameters) = this(x, x)
-  require (b  >= 0)
+  def this()(implicit p: Parameters) = this(BufferParams.default)
-  require (ar >= 0)
-  require (r  >= 0)
 
   val node = AXI4AdapterNode(
     masterFn = { p => p },
-    slaveFn  = { p => p.copy(minLatency = p.minLatency + min(1,min(aw,ar)) + min(1,min(r,b))) })
+    slaveFn  = { p => p.copy(minLatency = p.minLatency + min(aw.latency,ar.latency) + min(r.latency,b.latency)) })
 
   lazy val module = new LazyModuleImp(this) {
     val io = new Bundle {
@@ -27,12 +31,20 @@ class AXI4Buffer(aw: Int = 2, w: Int = 2, b: Int = 2, ar: Int = 2, r: Int = 2, p
       val out = node.bundleOut
     }
 
+    def buffer[T <: Data](config: BufferParams, data: IrrevocableIO[T]): IrrevocableIO[T] = {
+      if (config.isDefined) {
+        Queue.irrevocable(data, config.depth, pipe=config.pipe, flow=config.flow)
+      } else {
+        data
+      }
+    }
+
     ((io.in zip io.out) zip (node.edgesIn zip node.edgesOut)) foreach { case ((in, out), (edgeIn, edgeOut)) =>
-      if (aw>0) { out.aw <> Queue(in .aw, aw, pipe && aw<2) } else { out.aw <> in .aw }
+      out.aw <> buffer(aw, in .aw)
-      if (w >0) { out.w  <> Queue(in .w,  w,  pipe && w <2) } else { out.w  <> in .w  }
+      out.w  <> buffer(w,  in .w)
-      if (b >0) { in .b  <> Queue(out.b,  b,  pipe && b <2) } else { in .b  <> out.b  }
+      in .b  <> buffer(b,  out.b)
-      if (ar>0) { out.ar <> Queue(in .ar, ar, pipe && ar<2) } else { out.ar <> in .ar }
+      out.ar <> buffer(ar, in .ar)
-      if (r >0) { in .r  <> Queue(out.r,  r,  pipe && r <2) } else { in .r  <> out.r  }
+      in .r  <> buffer(r,  out.r)
     }
   }
 }
@@ -40,13 +52,16 @@ class AXI4Buffer(aw: Int = 2, w: Int = 2, b: Int = 2, ar: Int = 2, r: Int = 2, p
 object AXI4Buffer
 {
   // applied to the AXI4 source node; y.node := AXI4Buffer(x.node)
-  def apply()                               (x: AXI4OutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AXI4OutwardNode = apply(2)(x)
+  def apply()                                  (x: AXI4OutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AXI4OutwardNode = apply(BufferParams.default)(x)
-  def apply(entries: Int)                   (x: AXI4OutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AXI4OutwardNode = apply(entries, true)(x)
+  def apply(z: BufferParams)                   (x: AXI4OutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AXI4OutwardNode = apply(z, z)(x)
-  def apply(entries: Int, pipe: Boolean)    (x: AXI4OutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AXI4OutwardNode = apply(entries, entries, pipe)(x)
+  def apply(aw: BufferParams, br: BufferParams)(x: AXI4OutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AXI4OutwardNode = apply(aw, aw, br, aw, br)(x)
-  def apply(aw: Int, br: Int)               (x: AXI4OutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AXI4OutwardNode = apply(aw, br, true)(x)
+  def apply(
-  def apply(aw: Int, br: Int, pipe: Boolean)(x: AXI4OutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AXI4OutwardNode = apply(aw, aw, br, aw, br, pipe)(x)
+    aw: BufferParams,
-  def apply(aw: Int, w: Int, b: Int, ar: Int, r: Int, pipe: Boolean = true)(x: AXI4OutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AXI4OutwardNode = {
+    w:  BufferParams,
-    val buffer = LazyModule(new AXI4Buffer(aw, w, b, ar, r, pipe))
+    b:  BufferParams,
+    ar: BufferParams,
+    r:  BufferParams)(x: AXI4OutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AXI4OutwardNode = {
+    val buffer = LazyModule(new AXI4Buffer(aw, w, b, ar, r))
     buffer.node := x
     buffer.node
   }

src/main/scala/uncore/axi4/Test.scala

@@ -25,7 +25,7 @@ class AXI4LiteFuzzRAM()(implicit p: Parameters) extends LazyModule
   val ram   = LazyModule(new AXI4RAM(AddressSet(0x0, 0x3ff)))
 
   model.node := fuzz.node
-  xbar.node  := TLDelayer(0.1)(TLBuffer(TLBufferParams.flow)(TLDelayer(0.2)(model.node)))
+  xbar.node  := TLDelayer(0.1)(TLBuffer(BufferParams.flow)(TLDelayer(0.2)(model.node)))
   ram.node   := AXI4Fragmenter(lite=true)(TLToAXI4(0, true )(xbar.node))
   gpio.node  := AXI4Fragmenter(lite=true)(TLToAXI4(0, false)(xbar.node))
 
@@ -48,7 +48,7 @@ class AXI4FullFuzzRAM()(implicit p: Parameters) extends LazyModule
   val ram   = LazyModule(new AXI4RAM(AddressSet(0x0, 0x3ff)))
 
   model.node := fuzz.node
-  xbar.node  := TLDelayer(0.1)(TLBuffer(TLBufferParams.flow)(TLDelayer(0.2)(model.node)))
+  xbar.node  := TLDelayer(0.1)(TLBuffer(BufferParams.flow)(TLDelayer(0.2)(model.node)))
   ram.node   := AXI4Fragmenter(lite=false, maxInFlight = 2)(TLToAXI4(4,false)(xbar.node))
   gpio.node  := AXI4Fragmenter(lite=false, maxInFlight = 5)(TLToAXI4(4,true )(xbar.node))
 
@@ -72,7 +72,7 @@ class AXI4FuzzMaster()(implicit p: Parameters) extends LazyModule
   node :=
     TLToAXI4(4)(
     TLDelayer(0.1)(
-    TLBuffer(TLBufferParams.flow)(
+    TLBuffer(BufferParams.flow)(
     TLDelayer(0.1)(
     model.node))))
 
@@ -94,7 +94,7 @@ class AXI4FuzzSlave()(implicit p: Parameters) extends LazyModule
   ram.node :=
     TLFragmenter(4, 16)(
     TLDelayer(0.1)(
-    TLBuffer(TLBufferParams.flow)(
+    TLBuffer(BufferParams.flow)(
     TLDelayer(0.1)(
     AXI4ToTL()(
     AXI4Fragmenter()(

src/main/scala/uncore/tilelink2/Buffer.scala

@@ -8,33 +8,16 @@ import config._
 import diplomacy._
 import scala.math.{min,max}
 
-case class TLBufferParams(depth: Int, flow: Boolean, pipe: Boolean)
-{
-  require (depth >= 0)
-  def isDefined = depth > 0
-  def latency = if (isDefined && !flow) 1 else 0
-}
-
-object TLBufferParams
-{
-  implicit def apply(depth: Int): TLBufferParams = TLBufferParams(depth, false, false)
-
-  val default = TLBufferParams(2)
-  val none    = TLBufferParams(0)
-  val flow    = TLBufferParams(1, true, false)
-  val pipe    = TLBufferParams(1, false, true)
-}
-
 class TLBuffer(
-  a: TLBufferParams,
+  a: BufferParams,
-  b: TLBufferParams,
+  b: BufferParams,
-  c: TLBufferParams,
+  c: BufferParams,
-  d: TLBufferParams,
+  d: BufferParams,
-  e: TLBufferParams)(implicit p: Parameters) extends LazyModule
+  e: BufferParams)(implicit p: Parameters) extends LazyModule
 {
-  def this(ace: TLBufferParams, bd: TLBufferParams)(implicit p: Parameters) = this(ace, bd, ace, bd, ace)
+  def this(ace: BufferParams, bd: BufferParams)(implicit p: Parameters) = this(ace, bd, ace, bd, ace)
-  def this(abcde: TLBufferParams)(implicit p: Parameters) = this(abcde, abcde)
+  def this(abcde: BufferParams)(implicit p: Parameters) = this(abcde, abcde)
-  def this()(implicit p: Parameters) = this(TLBufferParams.default)
+  def this()(implicit p: Parameters) = this(BufferParams.default)
 
   val node = TLAdapterNode(
     clientFn  = { p => p.copy(minLatency = p.minLatency + b.latency + c.latency) },
@@ -46,7 +29,7 @@ class TLBuffer(
       val out = node.bundleOut
     }
 
-    def buffer[T <: Data](config: TLBufferParams, data: DecoupledIO[T]): DecoupledIO[T] = {
+    def buffer[T <: Data](config: BufferParams, data: DecoupledIO[T]): DecoupledIO[T] = {
       if (config.isDefined) {
         Queue(data, config.depth, pipe=config.pipe, flow=config.flow)
       } else {
@@ -77,15 +60,15 @@ class TLBuffer(
 object TLBuffer
 {
   // applied to the TL source node; y.node := TLBuffer(x.node)
-  def apply()                                       (x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = apply(TLBufferParams.default)(x)
+  def apply()                                   (x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = apply(BufferParams.default)(x)
-  def apply(abcde: TLBufferParams)                  (x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = apply(abcde, abcde)(x)
+  def apply(abcde: BufferParams)                (x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = apply(abcde, abcde)(x)
-  def apply(ace: TLBufferParams, bd: TLBufferParams)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = apply(ace, bd, ace, bd, ace)(x)
+  def apply(ace: BufferParams, bd: BufferParams)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = apply(ace, bd, ace, bd, ace)(x)
   def apply(
-      a: TLBufferParams,
+      a: BufferParams,
-      b: TLBufferParams,
+      b: BufferParams,
-      c: TLBufferParams,
+      c: BufferParams,
-      d: TLBufferParams,
+      d: BufferParams,
-      e: TLBufferParams)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = {
+      e: BufferParams)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = {
     val buffer = LazyModule(new TLBuffer(a, b, c, d, e))
     buffer.node := x
     buffer.node

src/main/scala/uncore/tilelink2/ToAHB.scala

@@ -25,12 +25,29 @@ case class TLToAHBNode() extends MixedAdapterNode(TLImp, AHBImp)(
         nodePath           = s.nodePath,
         supportsGet        = s.supportsRead,
         supportsPutFull    = s.supportsWrite, // but not PutPartial
-        fifoId             = Some(0)) // a common FIFO domain
+        fifoId             = Some(0))
     }
     TLManagerPortParameters(managers, beatBytes, 1, 1)
   })
 
-class TLToAHB(val combinational: Boolean = true)(implicit p: Parameters) extends LazyModule
+class AHBControlBundle(params: TLEdge) extends util.GenericParameterizedBundle(params)
+{
+  val full   = Bool()
+  val send   = Bool() // => full+data
+  val first  = Bool()
+  val last   = Bool()
+  val write  = Bool()
+  val size   = UInt(width = params.bundle.sizeBits)
+  val source = UInt(width = params.bundle.sourceBits)
+  val hsize  = UInt(width = AHBParameters.sizeBits)
+  val hburst = UInt(width = AHBParameters.burstBits)
+  val addr   = UInt(width = params.bundle.addressBits)
+  val data   = UInt(width = params.bundle.dataBits)
+}
+
+// The input side has either a flow queue (aFlow=true) or a pipe queue (aFlow=false)
+// The output side always has a flow queue
+class TLToAHB(val aFlow: Boolean = false)(implicit p: Parameters) extends LazyModule
 {
   val node = TLToAHBNode()
 
@@ -46,82 +63,129 @@ class TLToAHB(val combinational: Boolean = true)(implicit p: Parameters) extends
       val lgMax = log2Ceil(maxTransfer)
       val lgBytes = log2Ceil(beatBytes)
 
-      // AHB has no cache coherence
+      // Initial FSM state
-      in.b.valid := Bool(false)
+      val resetState = Wire(new AHBControlBundle(edgeIn))
-      in.c.ready := Bool(true)
+      resetState.full  := Bool(false)
-      in.e.ready := Bool(true)
+      resetState.send  := Bool(false)
+      resetState.first := Bool(true)
+      // These are needed to appease AHB VIP:
+      resetState.hsize := UInt(0)
+      resetState.hburst:= UInt(0)
+      resetState.addr  := UInt(0)
+
+      // The stages of the combinational pipeline
+      val reg  = RegInit(resetState)
+      val send = Wire(init = reg)
+      val step = Wire(init = send)
+      val next = Wire(init = step)
+      reg := next
+
+      // Advance the FSM based on the result of this AHB beat
+      when (send.send && !out.hreadyout) /* retry AHB */ {
+        step.full  := Bool(true)
+        step.send  := Bool(true)
+      } .elsewhen (send.full && !send.send) /* retry beat */ {
+        step.full  := Bool(true)
+        step.send  := Bool(false)
+      } .elsewhen (send.full && !send.last) /* continue burst */ {
+        step.full  := Bool(true)
+        step.send  := Bool(false) // => looks like a retry to injector
+        step.first := Bool(false)
+        step.last  := (if (lgBytes + 1 >= lgMax) Bool(true) else
+                       !((UIntToOH1(send.size, lgMax) & ~send.addr) >> (lgBytes + 1)).orR())
+        step.addr  := Cat(send.addr(edgeIn.bundle.addressBits-1, lgMax), send.addr(lgMax-1, 0) + UInt(beatBytes))
+      } .otherwise /* new burst */ {
+        step.full  := Bool(false)
+        step.send  := Bool(false)
+        step.first := Bool(true)
+      }
+
+      val d_block = Wire(Bool())
+      val pre  = if (aFlow) reg else step
+      val post = if (aFlow) send else next
+
+      // Transform TL size into AHB hsize+hburst
+      val a_sizeDelta = Cat(UInt(0, width = 1), in.a.bits.size) - UInt(lgBytes+1)
+      val a_singleBeat = Bool(lgBytes >= lgMax) || a_sizeDelta(edgeIn.bundle.sizeBits)
+      val a_logBeats1 = a_sizeDelta(edgeIn.bundle.sizeBits-1, 0)
+
+      // Pulse this every time we commit to sending an AHB request
+      val a_commit = Wire(Bool())
+
+      // Inject A channel into FSM
+      when (pre.send) /* busy */ {
+        a_commit := Bool(false)
+        in.a.ready := Bool(false)
+      } .elsewhen (pre.full) /* retry beat (or continue burst) */ {
+        post.send  := !d_block && (!pre.write || in.a.valid)
+        post.data  := in.a.bits.data
+        a_commit   := !d_block && !pre.write // only read beats commit to a D beat answer
+        in.a.ready := !d_block && pre.write
+      } .otherwise /* new burst */ {
+        a_commit := in.a.fire() // every first beat commits to a D beat answer
+        in.a.ready := !d_block
+        when (in.a.fire()) {
+          post.full  := Bool(true)
+          post.send  := Bool(true)
+          post.last  := a_singleBeat
+          post.write := edgeIn.hasData(in.a.bits)
+          post.size  := in.a.bits.size
+          post.source:= in.a.bits.source
+          post.hsize := Mux(a_singleBeat, in.a.bits.size, UInt(lgBytes))
+          post.hburst:= Mux(a_singleBeat, BURST_SINGLE, (a_logBeats1<<1) | UInt(1))
+          post.addr  := in.a.bits.address
+          post.data  := in.a.bits.data
+        }
+      }
+
+      out.hmastlock := Bool(false) // for now
+      out.htrans    := Mux(send.send, Mux(send.first, TRANS_NONSEQ, TRANS_SEQ), Mux(send.first, TRANS_IDLE, TRANS_BUSY))
+      out.hsel      := send.send || !send.first
+      out.hready    := out.hreadyout
+      out.hwrite    := send.write
+      out.haddr     := send.addr
+      out.hsize     := send.hsize
+      out.hburst    := send.hburst
+      out.hprot     := PROT_DEFAULT
+      out.hwdata    := RegEnable(send.data, out.hreadyout)
 
       // We need a skidpad to capture D output:
       // We cannot know if the D response will be accepted until we have
       // presented it on D as valid.  We also can't back-pressure AHB in the
-      // data phase.  Therefore, we must have enough space to save the data
+      // data phase.  Therefore, we must have enough space to save the all
-      // phase result.  Whenever we have a queued response, we can not allow
+      // commited AHB requests (A+D phases = 2). To decouple d_ready from
-      // AHB to present new responses, so we must quash the address phase.
+      // a_ready and htrans, we add another entry for aFlow=false.
+      val depth = if (aFlow) 2 else 3
       val d = Wire(in.d)
-      in.d <> Queue(d, 1, flow = true)
+      in.d <> Queue(d, depth, flow=true)
-      val a_quash = in.d.valid && !in.d.ready
+      assert (!d.valid || d.ready)
+
+      val d_flight = RegInit(UInt(0, width = 2))
+      assert (d_flight <= UInt(depth))
+      d_flight := d_flight + a_commit.asUInt - in.d.fire().asUInt
+      d_block := d_flight >= UInt(depth)
 
-      // Record what is coming out in d_phase
       val d_valid   = RegInit(Bool(false))
-      val d_hasData = Reg(Bool())
       val d_error   = Reg(Bool())
-      val d_addr_lo = Reg(UInt(width = lgBytes))
+      val d_write   = RegEnable(send.write,  out.hreadyout)
-      val d_source  = Reg(UInt())
+      val d_source  = RegEnable(send.source, out.hreadyout)
-      val d_size    = Reg(UInt())
+      val d_addr    = RegEnable(send.addr,   out.hreadyout)
+      val d_size    = RegEnable(send.size,   out.hreadyout)
 
-      when (out.hreadyout) { d_error := d_error || out.hresp }
+      when (out.hreadyout) {
-      when (d.fire()) { d_valid := Bool(false) }
+        d_valid := send.send && (send.last || !send.write)
+        when (out.hresp)  { d_error := d_write }
+        when (send.first) { d_error := Bool(false) }
+      }
 
       d.valid := d_valid && out.hreadyout
-      d.bits  := edgeIn.AccessAck(d_addr_lo, UInt(0), d_source, d_size, out.hrdata, out.hresp || d_error)
+      d.bits  := edgeIn.AccessAck(d_addr, UInt(0), d_source, d_size, out.hrdata, out.hresp || d_error)
-      d.bits.opcode := Mux(d_hasData, TLMessages.AccessAckData, TLMessages.AccessAck)
+      d.bits.opcode := Mux(d_write, TLMessages.AccessAck, TLMessages.AccessAckData)
 
-      // We need an irrevocable input for AHB to stall on read bursts
+      // AHB has no cache coherence
-      // We also need the values to NOT change when valid goes low => 1 entry only
+      in.b.valid := Bool(false)
-      val a = Queue(in.a, 1, flow = combinational, pipe = !combinational)
+      in.c.ready := Bool(true)
-      val a_valid = a.valid && !a_quash
+      in.e.ready := Bool(true)
-
-      // This is lot like TLEdge.firstlast, but counts beats also for single-beat TL types
-      val a_size = edgeIn.size(a.bits)
-      val a_beats1 = UIntToOH1(a_size, lgMax) >> lgBytes
-      val a_counter = RegInit(UInt(0, width = log2Up(maxTransfer/beatBytes)))
-      val a_counter1 = a_counter - UInt(1)
-      val a_first = a_counter === UInt(0)
-      val a_last = a_counter === UInt(1) || a_beats1 === UInt(0)
-      val a_offset = (a_beats1 & ~a_counter1) << lgBytes
-      val a_hasData = edgeIn.hasData(a.bits)
-
-      // Expand no-data A-channel requests into multiple beats
-      a.ready := (a_hasData || a_last) && out.hreadyout && !a_quash
-      when (a_valid && out.hreadyout) {
-        a_counter := Mux(a_first, a_beats1, a_counter1)
-        d_valid := !a_hasData || a_last
-        // Record what will be in the data phase
-        when (a_first) {
-          d_hasData := !a_hasData
-          d_error   := Bool(false)
-          d_addr_lo := a.bits.address
-          d_source  := a.bits.source
-          d_size    := a.bits.size
-        }
-      }
-
-      // Transform TL size into AHB hsize+hburst
-      val a_size_bits = a_size.getWidth
-      val a_sizeDelta = Cat(UInt(0, width = 1), a_size) - UInt(lgBytes+1)
-      val a_singleBeat = a_sizeDelta(a_size_bits)
-      val a_logBeats1 = a_sizeDelta(a_size_bits-1, 0)
-
-      out.hmastlock := Bool(false) // for now
-      out.htrans    := Mux(a_valid, Mux(a_first, TRANS_NONSEQ, TRANS_SEQ), Mux(a_first, TRANS_IDLE, TRANS_BUSY))
-      out.hsel      := a_valid || !a_first
-      out.hready    := out.hreadyout
-      out.hwrite    := a_hasData
-      out.haddr     := a.bits.address | a_offset
-      out.hsize     := Mux(a_singleBeat, a.bits.size, UInt(lgBytes))
-      out.hburst    := Mux(a_singleBeat, BURST_SINGLE, (a_logBeats1<<1) | UInt(1))
-      out.hprot     := PROT_DEFAULT
-      out.hwdata    := RegEnable(a.bits.data, a.fire())
     }
   }
 }
@@ -129,8 +193,8 @@ class TLToAHB(val combinational: Boolean = true)(implicit p: Parameters) extends
 object TLToAHB
 {
   // applied to the TL source node; y.node := TLToAHB()(x.node)
-  def apply(combinational: Boolean = true)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AHBOutwardNode = {
+  def apply(aFlow: Boolean = true)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AHBOutwardNode = {
-    val ahb = LazyModule(new TLToAHB(combinational))
+    val ahb = LazyModule(new TLToAHB(aFlow))
     ahb.node := x
     ahb.node
   }

src/main/scala/uncore/tilelink2/ToAPB.scala

@@ -31,7 +31,9 @@ case class TLToAPBNode() extends MixedAdapterNode(TLImp, APBImp)(
     TLManagerPortParameters(managers, beatBytes, 1, 0)
   })
 
-class TLToAPB(combinational: Boolean = true)(implicit p: Parameters) extends LazyModule
+// The input side has either a flow queue (aFlow=true) or a pipe queue (aFlow=false)
+// The output side always has a flow queue
+class TLToAPB(val aFlow: Boolean = true)(implicit p: Parameters) extends LazyModule
 {
   val node = TLToAPBNode()
 
@@ -60,7 +62,7 @@ class TLToAPB(combinational: Boolean = true)(implicit p: Parameters) extends Laz
       in.d <> Queue(d, 1, flow = true)
 
       // We need an irrevocable input for APB to stall
-      val a = Queue(in.a, 1, flow = combinational, pipe = !combinational)
+      val a = Queue(in.a, 1, flow = aFlow, pipe = !aFlow)
 
       val a_enable = RegInit(Bool(false))
       val a_sel    = a.valid && RegNext(!in.d.valid || in.d.ready)
@@ -90,8 +92,8 @@ class TLToAPB(combinational: Boolean = true)(implicit p: Parameters) extends Laz
 object TLToAPB
 {
   // applied to the TL source node; y.node := TLToAPB()(x.node)
-  def apply(combinational: Boolean = true)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): APBOutwardNode = {
+  def apply(aFlow: Boolean = true)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): APBOutwardNode = {
-    val apb = LazyModule(new TLToAPB(combinational))
+    val apb = LazyModule(new TLToAPB(aFlow))
     apb.node := x
     apb.node
   }

src/main/scala/unittest/Configs.scala

@@ -12,9 +12,11 @@ class WithUncoreUnitTests extends Config((site, here, up) => {
     implicit val p = q
     Seq(
       Module(new uncore.tilelink2.TLFuzzRAMTest),
-      Module(new uncore.ahb.AHBBridgeTest),
+      Module(new uncore.ahb.AHBBridgeTest(true)),
-      Module(new uncore.ahb.AHBNativeTest),
+      Module(new uncore.ahb.AHBNativeTest(true)),
-      Module(new uncore.apb.APBBridgeTest),
+      Module(new uncore.ahb.AHBNativeTest(false)),
+      Module(new uncore.apb.APBBridgeTest(true)),
+      Module(new uncore.apb.APBBridgeTest(false)),
       Module(new uncore.axi4.AXI4LiteFuzzRAMTest),
       Module(new uncore.axi4.AXI4FullFuzzRAMTest),
       Module(new uncore.axi4.AXI4BridgeTest)) }